Chemicals are added to processing streams to accomplish a wide variety of goals. These chemicals may be detergents, surfactants, bleaching agents, biocides as well as a variety of other chemicals. A commonly used method to dispense chemicals into a process stream is to start with a solid material and dissolve a portion of the solid material and then inject the formed solution into the process stream. This is a relatively simple way of adding a soluble solid chemical to a liquid stream.
In actuality, this dispensing method has many different problems. Typically the water is added to one end of a holding tank and passes through the solid and is recovered from the opposite end of the holding tank. Because of the nature of water flow, it tends to channel through the bed of solid material providing limited contact between the water and the solid.
Further, solubility changes dramatically with temperature. As a result, the concentration of the liquid added to the process stream is extremely inconsistent. Variations of 50% to 60% are common. Variations in concentration is at best wasteful. More likely it can lead to much worse consequences. With biocide treatment concentration variation can cause dramatic increases in bacteria levels. This can damage equipment and products.
The apparatus typically used in these dispensing systems is also problematic. Generally the tanks are pressurized. Pressurization forces the water through the tank into the process stream. A pressurized tank of dissolved processing chemicals is inherently dangerous. Further, the tank generally must be relatively tall, otherwise there will not be adequate physical contact between the liquid and the solid. Frequently these need to be fifteen feet or taller which requires a special room. The tank height and its pressurization also makes it more difficult to load the tank with additional solid chemical. The system generally must be shut down and at least partially drained to add additional solid chemical. Draining concentration and liquid solutions to cover is problematic. It can cause environmental damage and can harm bacteria used in waste water treatment facilities.
The present invention is premised on the realization that a uniformed concentration of dissolved chemical can be obtained in an aqueous stream by recirculating an aqueous stream through a tank holding the solid chemical. By passing the solution repeatedly through the tank, a uniform concentration can be achieved at atmospheric pressure. Further, a heater is employed within the recirculation loop of the apparatus to establish a desired temperature. This stabilizes the concentration of the solute in the solution, again improving the consistency of the concentration.
In a preferred embodiment, the tank employs a gravel bed or other water dispersion system at the base of the tank. The water is injected through the gravel bed distributing the water evenly across the diameter of the bed. The solution is recovered from the top of the bed after passing through the solid material. This provides for even distribution and avoids the channeling incurred with prior art apparatus.
Further, the apparatus of the present invention, since it uses a recirculation loop, employs a separate pump allowing the tank to be maintained at atmospheric pressure. This eliminates the inherent safety problem associated with maintaining a pressurized tank of dissolved chemicals.
The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which: